1. Field of the Invention
The present invention relates to an ultrasonic cleaning device fault detector, particularly to an ultrasonic cleaning device fault detector which is suitable for use at producing semiconductors.
2. Description of Related Art
During the production of semiconductor wafers, the wafers or part of the apparatus used need cleaning. Cleaning is usually performed by ultrasonic waves. For this, ionized liquid is filled into a vessel with a vibrating device on a periphery thereof. The vibrating device generates ultrasonic waves, and the ionized liquid serves as a medium for the ultrasonic waves. Thus, after placing an object to be cleaned in the vessel, dirt of various kinds is removed from the object. However, if the vibrating device fails, e.g., if output thereof is too low or entirely absent, no effective cleaning is performed. Therefore a detector is required to monitor proper functioning of the vibrating device.
Conventionally, monitoring a cleaning device is performed by a detector sensing ultrasonic waves in the vessel, when the vibrating device is turned on. For detecting vibrations in the vessel, a mercury switch, a voltage detector or a special vibration-sensitive integrated circuit are used. However, all of these detector designs have the following shortcomings:
1. Installation is difficult: Since the detector needs to be fixed on the vessel, space has to be reserved for the detector when the vessel is designed. Otherwise, there is no way to install the detector on the vessel.
2. Interference by external noise. The detector not only senses waves in the vessel, but also electric noise and vibrations from other sources. Therefore, it is not possible to ascertain that vibrations inside the vessel have occurred.
It is an object of the present invention to provide an ultrasonic cleaning device fault detector which is not easily subjected to noise and which is able to recognize a defect of an ultrasonic cleaning device correctly.
Another object of the present invention is to provide an ultrasonic cleaning device fault detector which is easy to install and offers increased flexibility.
The present invention can be more fully understood by reference to the following description and accompanying drawings.